[Show abstract][Hide abstract] ABSTRACT: We report a thermally activated metastability in a GaAs double quantum dot
exhibiting real-time charge switching in diamond shaped regions of the charge
stability diagram. Accidental charge traps and sensor back action are excluded
as the origin of the switching. We present an extension of the canonical double
dot theory based on an intrinsic, thermal electron exchange process through the
reservoirs, giving excellent agreement with the experiment. The electron spin
is randomized by the exchange process, thus facilitating fast, gate-controlled
spin initialization. At the same time, this process sets an intrinsic upper
limit to the spin relaxation time.
[Show abstract][Hide abstract] ABSTRACT: We present a method for determining correlations in a gas of indirect
excitons in a semiconductor quantum well structure. The method involves
subjecting the excitons to a periodic electrostatic potential that causes
modulations of the exciton density and photoluminescence (PL). Experimentally
measured amplitudes of energy and intensity modulations of exciton PL serve as
an input to a theoretical estimate of the exciton correlation parameter and
temperature. We also present a proof-of-principle demonstration of the method
for determining the correlation parameter and discuss how its accuracy can be
Physical Review B 08/2015; 92(11). DOI:10.1103/PhysRevB.92.115311 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Planar ultrathin InAs-channel MOSFETs were demonstrated on Si substrates with gate lengths (Lg) as small as 20 nm. The III-V epitaxial buffer layers were grown on 300 mm Si substrates by metal-organic chemical vapor deposition (MOCVD) and the subsequent InAlAs bottom barriers and InAs channel were grown by molecular beam epitaxy (MBE). The devices at 20 nm Lg show high transconductance, ∼2.0 mS/μm at VDS=0.5V.
International Symposium on VLSI Technology, Systems, and Applications, Proceedings 06/2015; 2015. DOI:10.1109/VLSI-TSA.2015.7117566
[Show abstract][Hide abstract] ABSTRACT: We review development of In(Ga)As-channel MOSFETs. InAs and InGaAs channels, combined with thin gate dielectrics, provide high transconductance, but off-state leakage can be high due to bandband tunneling currents. This leakage is reduced through thin 2.5-3nm channels, and through InGaAs or InP vertical field spacers in the raised source and drain. Devices with 2.7nm InAs channels and lightly-doped InGaAs source/drain spacers, at 25nm Lg, provide a record 0.5mA/μm Ion at 100nA/μm Ioff and 500mV VDD. 1 μm Lg FETs show 61mV/decade subthreshold swing at VDD=0.1 V. Targeting the LP specification, we have developed InGaAschannel MOSFETs with lightly-doped InP wide-bandgap source/drain spacer layers. At 30nm gate length, these show a minimum 60 pA/μm Ioff, approximately 100:1 smaller than a similar device using InGaAs source/drain spacers. A FET using InP spacers, with 45 nm gate length, shows 0.15 mA/μm Ion at 1nA/μm Ioff and 500mV VDD.
[Show abstract][Hide abstract] ABSTRACT: We report InGaAs-channel MOSFETs using recessed InP spacer layers in the regrown source and drain. By replacing narrow band-gap InGaAs with wide band-gap InP within the high-field region near the drain end of the channel, band-to-band tunneling (BTBT) leakage is significantly reduced. A 30 nm gate length device using InP spacers shows a minimum Ioff∼60 pA/μm, approximately 100:1 smaller than a similar device using InGaAs source/drain spacers. A FET using InP spacers, with 45 nm gate length, and with a 3 nm ZrO2 gate oxide shows Ion=150 μA/μm at Ioff=1 nA/μm and VDS=0.5 V. The low off-state leakage current observed with InP source/drain spacers makes InGaAs MOS technology viable for low-power logic.
Electron Devices Meeting, 1988. IEDM '88. Technical Digest., International 02/2015; 2015:25.4.1-25.4.4. DOI:10.1109/IEDM.2014.7047107
[Show abstract][Hide abstract] ABSTRACT: At low temperatures, indirect excitons formed at the in-plane electron-hole
interface in a coupled quantum well structure undergo a spontaneous transition
into a spatially modulated state. We report on the control of the instability
wavelength, measurement of the dynamics of the exciton emission pattern, and
observation of the fluctuation and commensurability effect of the exciton
density wave. We found that fluctuations are strongly suppressed when the
instability wavelength is commensurate with defect separation along the exciton
density wave. The commensurability effect is also found in numerical
simulations within the model describing the exciton density wave in terms of an
instability due to stimulated processes.
Physical Review B 02/2015; 91(24). DOI:10.1103/PhysRevB.91.245302 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Because InGaAs has a small bandgap, InGaAs MOSFETs are vulnerable to large band-to-band tunneling currents, arising near the drain end of the channel. This sets a minimum off-state leakage current, and can render the device unsuitable for VLSI applications at sub-10-nm gate lengths. Here we report two techniques to reduce band-to-band tunneling leakage in InGaAs MOSFETs. By using either a recessed InP wide bandgap spacer in the regrown source/drain region or, alternatively, an InP channel cap on top of InGaAs channel, off-state leakage can be reduced to 1 nA/μm for 22 nm gate length devices. These two techniques pave the way for application of III-V InGaAs MOSFETs in low power logic.
[Show abstract][Hide abstract] ABSTRACT: Collective vibrations of proteins, rotations of small molecules, excitations
of high-temperature superconductors, and electronic transitions in
semiconductor nanostructures occur with characteristic frequencies between 1
and 10 THz. Applications to medicine, communications, security and other fields
are emerging. However, mapping the coldest parts of the universe has been the
largest driver for developing THz detectors. The result is a family of
exquisitely-sensitive detectors requiring sub-4K temperatures. For earthbound
THz science and technology, sensitivity remains important but many applications
require high speed and operating temperatures. Room-temperature Schottky diodes
enable some of these applications. Here we demonstrate a new type of detector
in which THz radiation excites a collective oscillation of ~25,000 electrons
between two gates in a microscopic four terminal transistor. The energy
dissipates into other modes of the electron gas, warming it and changing the
source-drain resistance. The detector shows amplifier-limited rise times near 1
ns and has detected THz laser radiation at temperatures up to 120K. The
frequency of the collective oscillation tunes with small gate voltages. The
first-generation tunable antenna-coupled intersubband Terahertz (TACIT)
detectors tune between 1.5 and 2 THz with voltages <2V.
[Show abstract][Hide abstract] ABSTRACT: We report MOSFETs with 25-nm gate length (Lg), extremely thin 2.5 nm InAs channels and 0.7/3.0 nm (physical) Al2OxNy/ZrO2 gate dielectrics, and 12 nm In0.53Ga0.47As vertical spacers in the raised epitaxial source/drain. The FETs establish key new DC performance records, at VLSI-relevant gate lengths (25 nm), including 0.50 mA/μm on-current (at 100 nA/μm Ioff and 0.5 V VDD) and 77 mV/dec. subthreshold swing (SS) at VDS=0.5 V. At 1 μm Lg and VDS=0.1 V, the minimum subthreshold swing is 61 mV/dec., a record low for InAs/InGaAs, indicating high interface quality.
Digest of Technical Papers - Symposium on VLSI Technology 09/2014; DOI:10.1109/VLSIT.2014.6894363
[Show abstract][Hide abstract] ABSTRACT: Solid-state qubits have recently advanced to the level that enables them,
in-principle, to be scaled-up into fault-tolerant quantum computers. As these
physical qubits continue to advance, meeting the challenge of realising a
quantum machine will also require the engineering of new classical hardware and
control architectures with complexity far beyond the systems used in today's
few-qubit experiments. Here, we report a micro-architecture for controlling and
reading out qubits during the execution of a quantum algorithm such as an error
correcting code. We demonstrate the basic principles of this architecture in a
configuration that distributes components of the control system across
different temperature stages of a dilution refrigerator, as determined by the
available cooling power. The combined setup includes a cryogenic
field-programmable gate array (FPGA) controlling a switching matrix at 20
millikelvin which, in turn, manipulates a semiconductor qubit.
[Show abstract][Hide abstract] ABSTRACT: Advances in thin film growth technology have enabled the selective engineering of material properties to improve the thermoelectric figure of merit and thus the efficiency of energy conversion devices. Precise characterization at the operational temperature of novel thermoelectric materials is crucial to evaluate their performance and optimize their behavior. However, measurements on thin film devices are subject to complications from the growth substrate, non-ideal contacts, and other thermal and electrical parasitic effects. In this manuscript, we determine the cross-plane thermoelectric material properties in a single measurement of a 25 μm InGaAs thin film with embedded ErAs (0.2%) nanoparticles using the bipolar transient Harman method in conjunction with thermoreflectance thermal imaging at temperatures up to 550 K. This approach eliminates discrepancies and potential device degradation from the multiple measurements necessary to obtain individual material parameters. In addition, we present a strategy for optimizing device geometry to mitigate the effect of both electrical and thermal parasitics during the measurement. Finite element method simulations are utilized to analyze non-uniform current and temperature distributions over the device area as well as the three dimensional current path for accurate extraction of material properties from the thermal images. Results are compared with independent in-plane and 3ω measurements of thermoelectric material properties for the same material composition and are found to match reasonably well; the obtained figure of merit matches within 15% at room and elevated temperatures.
[Show abstract][Hide abstract] ABSTRACT: We report the observation of spin currents and spin polarization textures in opti- cally generated indirect excitons. The textures are observed in linear and circular polarizations and are controlled by magnetic fields.
[Show abstract][Hide abstract] ABSTRACT: We experimentally demonstrate an order of magnitude higher radiated power from a 1550 nm photomixer with plasmonic contact electrodes in comparison with an analogous photomixer without plasmonic contact electrodes in the 0.25-2.5 THz frequency range.
[Show abstract][Hide abstract] ABSTRACT: We report on self-assembled ErSb nanowires in a GaSb matrix that show a strong polarization-sensitive THz response. The nanowires behave like a polarizer. Their orientation and shape can be engineered by the growth conditions.
[Show abstract][Hide abstract] ABSTRACT: While the growth of III-As and III-P semiconductors is well-established, and their transport properties well-understood, the performance of high-frequency and VLSI electron devices can still be substantially improved. Here we review design principles, experimental efforts, and intermediate results, in the development of nm and THz electron devices, including nm InAs/InGaAs planar MOSFETs and finFETs for VLSI, InGaAs/InP DHBTs for 0.1-1 THz wireless communications and imaging, and ~5nm InAs/InGaAs Schottky diodes for mid-IR mixing.
2014 72nd Annual Device Research Conference (DRC); 06/2014
[Show abstract][Hide abstract] ABSTRACT: Multielectron spin qubits are demonstrated, and performance examined by comparing coherent exchange oscillations in coupled single-electron and multielectron quantum dots, measured in the same device. Fast (>1 GHz) exchange oscillations with a quality factor Q∼15 are found for the multielectron case, compared to Q∼2 for the single-electron case, the latter consistent with experiments in the literature. A model of dephasing that includes voltage and hyperfine noise is developed that is in good agreement with both single- and multielectron data, though in both cases additional exchange-independent dephasing is needed to obtain quantitative agreement across a broad parameter range.
[Show abstract][Hide abstract] ABSTRACT: Quantum-dot spin qubits characteristically use oscillating magnetic or electric fields, or quasi-static Zeeman field gradients, to realize full qubit control. For the case of three confined electrons, exchange interaction between two pairs allows qubit rotation around two axes, hence full control, using only electrostatic gates. Here, we report initialization, full control, and single-shot readout of a three-electron exchange-driven spin qubit. Control via the exchange interaction is fast, yielding a demonstrated 75 qubit rotations in less than 2 ns. Measurement and state tomography are performed using a maximum-likelihood estimator method, allowing decoherence, leakage out of the qubit state space, and measurement fidelity to be quantified. The methods developed here are generally applicable to systems with state leakage, noisy measurements and non-orthogonal control axes.